The present invention relates to equalizing an input signal, and more particularly, to an adaptive equalization apparatus with an equalization parameter setting adaptively adjusted according to edges of an equalizer output monitored in a real-time manner and related method thereof.
With regard one application using a cable (e.g., an HDMI cable) to interconnect a transmitter end and a receiver end, the cable length is not required to be a fixed value. In other words, one user might use a cable of a first length to interconnect the transmitter end and the receiver end, while the other user might use a cable of a second length to interconnect the transmitter end and the receiver end. In general, the cable will affect the transmitted signal in amplitude and/or phase. Therefore, in a case where the transmitter ends output the same signal to respective receiver ends, the received signals at the receiver ends are not identical to each other due to the fact that the cable characteristics, such as the cable lengths, are not the same. For example, the cable has a limited channel bandwidth, and the inter-symbol interference (ISI) might occur to degrade the signal quality of the transmitted signal. An adaptive equalizer is generally implemented at the receiver end to adaptively reduce or eliminate the signal degradation caused by the cable.
Please refer to FIG. 1 in conjunction with FIG. 2. FIG. 1 illustrates an eye diagram of a received signal degraded by jitter according to the related art. FIG. 2 illustrates an eye diagram of a received signal degraded by inter-symbol interference according to the related art. As known to those skilled in the art, the eye diagram is a useful tool for the qualitative analysis of the digital signal transmission. In general, the eye diagram is an oscilloscope display of a digital signal, repetitively sampled to get a good representation of its behavior. As shown in FIG. 1, the exemplary eye diagram E1 is constructed by an overlay of a plurality of signal sequences S1, S2, S3 on the screen of an oscilloscope. As one can see, the width between transitions in the signal sequences S1, S2, S3 is equal to the same value (i.e., W1=W2=W3=W4=W5=W6); however, the transition timings of the signal sequences S1, S2, S3 are different due to jitter. With regard to the other eye diagram E2 shown in FIG. 2, it is constructed by an overlay of a plurality of signal sequences S1′, S2′, S3′ on the screen of an oscilloscope. As one can see, though the lengths of the signal sequences S1′, S2′, S3′ are the same (i.e., W1′+W2′=W3′+W4′=W5′+W6′), the width between transitions in the signal sequences S1, S2, S3 varies due to inter-symbol interference (i.e., W1′≠W2′, W3′≠W4′, and W5′≠W6′).
In the conventional design of the adaptive equalizer apparatus, an eye opening of the eye diagram is monitored using an eye-opening monitor to determine if the equalizer parameters should be adjusted. The signal degradation might be induced due to jitter and/or inter-symbol interference. However, the adaptive equalizer is only capable of improving the quality of a signal degraded by inter-symbol interference, and the conventional design of the adaptive equalizer apparatus does not discriminate signal degradation cause by inter-symbol interference from signal degradation caused by jitter. That is to say, the conventional eye-opening monitor has no capability of differentiating the interference sources of the transition variations R1 and R2 shown in FIG. 1 and FIG. 2. In a case where the signal degradation caused by jitter is mistakenly treated as signal degradation caused by inter-symbol interference through monitoring the eye opening of the eye diagram E1 in FIG. 1, the conventional adaptive equalizer is erroneously enabled to adjust the equalizer parameters, leading to worse signal quality of the received signal. As a result, the following signal processing (e.g., the clock and data recovery) applied to the equalizer output would fail, resulting in an unstable system.
In addition, as mentioned above, the equalizer parameters of the conventional adaptive equalizer are adaptively adjusted according to the result of monitoring the eye opening of the eye diagram, where the monitored eye diagram is an oscilloscope display of an accumulated result (i.e., an overlay) of a plurality of signal sequences rather than an instant result of a signal sequence. Furthermore, the adaptive equalizer is only capable of improving quality of a signal degraded by inter-symbol interference. That is, the conventional adaptive equalizer fails to improve quality of a signal degraded by jitter. Therefore, as the instant information of the inter-symbol interference cannot be derived from the monitored eye diagram constructed by an overlay of a plurality of signal sequences, the conventional adaptive equalizer fails to promptly tune the equalizer parameters in response to the inter-symbol interference for achieving an optimized equalizer output for following signal processing (e.g., the clock and data recovery).